Studies of the immune response of rats to Trichinella spiralis continue in an effort to define antigens of the parasite which can induce a measure of acquired immunity against the enteral phase. Prominence will be given to studies of the "rapid expulsion" reaction that is expressed against infections muscle stage larvae. Aside from defining the class(es) of immunoglobulin and the type(s) of cells which mediate this reaction, efforts will be made to define an intestinal factor (? inflammation) that is required for the full expression of rapid expulsion.